There are various kinds of color displays, and these color displays are in practical use. Flat type displays are roughly categorized into a self-luminous display such as a PDP (plasma display panel) and a non-luminous display represented by an LCD (liquid crystal display device). As the LCD which is the non-luminous display, a transmission LCD having a backlight disposed on a rear side of a liquid crystal panel is known.
FIG. 11 is a cross sectional view illustrating a general structure of the transmission LCD. The transmission LCD is arranged so that a backlight 110 is disposed on a rear side of a liquid crystal panel 100. The liquid crystal panel 100 is arranged so that: a liquid crystal layer 103 is disposed between a pair of transparent substrates 101 and 102, and polarization plates 104 and 105 are respectively provided on outer sides of the pair of transparent substrates 101 and 102. Further, a color filter 106 is provided in the liquid crystal panel 100, so that it is possible to realize color display.
Although not shown, an electrode layer and an alignment film are formed so as to be positioned more inwardly than the transparent substrates 101 and 102, and a voltage applied to the liquid crystal layer 103 is controlled, thereby controlling transmission quantities of light in the liquid crystal panel 100 for each pixel. That is, the transmission LCD controls, in the liquid crystal panel 110, the transmission quantities of light emitted from the backlight 110, thereby controlling a display.
As the backlight 110, a backlight emitting white light containing three wavelengths, i.e., R, G, and B wavelengths required in a color display is mainly used. With a color filter 106, transmittances of R, G, and B lights are adjusted, thereby arbitrarily setting a luminance and a hue of a pixel. As such a backlight 110, a white light source such as an electroluminescence (EL), a cold cathode fluorescent lamp (CCFL), and a light emitting diode (LED) is generally used.
In the liquid crystal panel 100, as illustrated in FIG. 12, a plurality of pixels are disposed in a matrix manner, and each pixel is generally constituted of three sub pixels. The sub pixels are disposed so as to respectively correspond to a red (R) filter layer, a green (G) filter layer, and a blue (B) filter layer in the color filter 106. Hereinafter, these sub pixels are respectively referred to as an R sub pixel, a G sub pixel, and a B sub pixel.
Each of the R sub pixel, the G sub pixel, and the B sub pixel selectively transmits light, out of white light generated by the backlight 110, whose waveband corresponds to the sub pixel (i.e., red, green, or blue light), and absorbs light whose waveband is out of the foregoing waveband.
As to light emitted from the backlight 110 in the transmission LCD arranged in the foregoing manner, transmission quantities of light are controlled for each pixel of the liquid crystal panel 100, so that it is natural that some light is absorbed by the liquid crystal panel 100. Further, each of the R, G, and B sub pixels also in the color filter 106 absorbs light, out of white light generated by the backlight 110, whose waveband is out of a waveband corresponding to the sub pixel. In this way, a general transmission LCD has a liquid crystal panel or a color filter which absorbs a large quantity of light, so that the LCD cannot efficiently use light emitted from the backlight. This raises such a problem that the backlight consumes much power.
As a technique for reducing power consumption of the transmission LCD, there is known a technique using an active backlight capable of adjusting a luminance in accordance with a display image (for example, Japanese Unexamined Patent Publication No. 65531/1999 (Tokukaihei 11-65531) (Publication date: Mar. 9, 1999)).
That is, Tokukaihei 11-65531 discloses a technique in which an active backlight capable of adjusting a luminance is used and a display of the LCD is controlled (a luminance is controlled) by controlling transmittances of the liquid crystal panel and the luminance of the active backlight thereby reducing power consumption of the backlight.
In the technique of Tokukaihei 11-65531, the luminance of the backlight is controlled so as to correspond to a maximum luminance value of an inputted image (inputted signals). Further, a transmittance of the liquid crystal panel is adjusted so as to correspond to the luminance of the backlight.
In this case, a transmittance of a sub pixel whose input signal has a maximum value is 100%, and also a transmittance of other sub pixel is less than 100% as a result of calculation based on a backlight value. Thus, when the image is entirely dark, the backlight is made dark, thereby reducing power consumption of the backlight.
In this way, according to Tokukaihei 11-65531, brightness of the backlight is suppressed to a minimum level in accordance with input signals R, G, and B of an input image, and the backlight is made dark, so that a transmittance of liquid crystal is accordingly increased. Thus, intensity of light absorbed by the liquid crystal panel is decreased, thereby reducing power consumption of the backlight.
However, according to the conventional arrangement, it is possible to reduce power consumption of the backlight by reducing intensity of light absorbed by the liquid crystal panel but it is impossible to reduce intensity of light absorbed by the color filter. Thus, if it is possible to reduce intensity of light absorbed by the color filter, it is possible to obtain such an effect that the power consumption is further reduced.